Aerodynamic trimmer head for use in flexible line rotary trimmers

ABSTRACT

An aerodynamic trimmer head assembly for use in flexible line rotary trimmers including a trimmer head having a curvilinear upper head surface and a shroud having a curvilinear portion extending over the head surface. A plurality of ribs extend downwardly and forwardly in the direction of rotation between the head surface and shroud defining a plurality of channels extending between portions of the upper head surface and shroud along curvilinear paths defined by the ribs. The channels define inlet openings in an upper portion of the shroud and outlet openings about the lower end portion thereof. During rotation of the head and shroud, air is drawn downwardly about the drive mechanism, through the channel inlets, into and through the channels and outwardly therefrom at a forward inclination about the line projecting from the housing thereby cooling the drive mechanism of the rotary trimmer and reducing aerodynamic drag on the line.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.13/217,193, filed Aug. 24, 2011 entitled “Aerodynamic Trimmer Head ForUse In Flexible Line Rotary Trimmers”, now U.S. Pat. No. 8,918,999,issued Dec. 30, 2014, which is a continuation-in-part of U.S. patentapplication Ser. No. 13/033,564, filed Feb. 23, 2011 entitled“Aerodynamic Trimmer Head For Use In Flexible Line Rotary Trimmers”, nowU.S. Pat. No. 8,910,388, issued Dec. 16, 2014, which is acontinuation-in-part of U.S. patent application Ser. No. 12/717,908,filed Mar. 4, 2010, now U.S. Pat. No. 8,567,073, issued Oct. 29, 2013and also entitled “Aerodynamic Trimmer Head For Use In Flexible LineRotary Trimmers”.

BACKGROUND OF THE INVENTION

The present invention relates to an improved trimmer head for use inflexible line rotary trimming devices used to trim grass, weeds andother vegetation. More particularly, the invention is directed to animprovement in the aerodynamics of the trimmer head so that with thesame drive input, the head will rotate faster than a conventionaltrimmer head, enhancing the cutting efficiency of the rapidly rotatingcutting line, or rotate at the same speed as a conventional head withless drive input, saving energy, while concurrently effecting a coolingof the batteries and/or drive mechanism of the trimmer to increase thelife thereof. The improved aerodynamics of the head in the presentinvention also has been found to reduce vibration and noise during use.

Trimmer heads used in flexible line rotary trimmers generally carry oneor two lengths of flexible nylon cutting line typically wrapped about aninterior spool with the ends of the line or lines projecting outwardlythrough opposed apertures in the side wall of the trimmer head. The headis threadably mounted on the end of an elongated shaft and rotated at ahigh velocity by a gas or electric motor so that the ends of the cuttingline project radially from the head and sever weeds or other vegetation.When cutting line projecting from the head breaks off or becomes overlyworn, it must be severed and fresh line extended from the spool throughthe line outlet eyelets in the side of the housing. Bump-feed type headssuch as those disclosed in U.S. Pat. Nos. 4,458,419, 4,959,904 and6,901,667, include a line feed-out mechanism which responds to theoperator intentionally bumping the rotating head against the groundduring use to feed out a measured length of fresh cutting line which istypically cut to the desired length by a knife blade projecting from ashield attached to the trimmer above the cutting head and spaced apredetermined distance from the perimeter of the trimmer head housing.Manual heads such as that disclosed in U.S. Pat. No. 7,275,324, do notinclude any such line feed-out mechanism. The spool must be manuallyrotated relative to the housing to pay out additional cutting line.Automatic heads such as that disclosed in U.S. Pat. No. 5,063,673,include a mechanism that detects a loss of mass in the cutting lineprojecting from the head during use and, without the need for any actionby the operator, pay out additional lengths of line from the spoolthrough the eyelets. Fixed line heads such as that disclosed in U.S.Pat. No. 6,928,741, utilize one or more relatively short lengths ofcutting line, typically under 12 inches in length, that project from thetrimmer head housing and are held proximate their inner ends by a linegripping mechanism disposed within the housing. The improvement of thepresent invention is adaptable for use with each of these types of headto improve the efficiency thereof and reduce noise and vibration.

SUMMARY OF THE INVENTION

Briefly, the present invention is directed to an improved trimmer headfor use in flexible line rotary trimmers that is more efficient, effectscooling of the trimmer drive mechanism and generates less noise andvibration than conventional trimmer heads. The trimmer head of thepresent invention preferably comprises a low profile housing, preferablyof a generally elliptical configuration. A spool for carrying one ormore lengths of cutting line can be mounted within the housing andpreferably configured such that the lower spool surface is generallycurvilinear and merges smoothly into the contour of the lower portion ofthe trimmer head. The outer surfaces of the upper and lower portions ofthe head define aerodynamic features in the form of surfaceirregularities therein configured to enhance the aerodynamics of thetrimmer head and reduce the drag on the head and line during use.

In one embodiment of the present invention, the outer surface of theupper portion of the housing is provided with a plurality of coordinatedarcuate troughs angularly disposed therein so as to draw air downwardly,during use, about the central axis of rotation of the trimmer head andonto the upper surface of the head where the air is moved outwardly anddownwardly therefrom by the troughs at a forward inclination in thedirection of rotation of the head and into the plane of the rotatingcutting line. The downward air flow will pass about the gear box in agasoline powered rotary trimmer, cooling the gears, or about the motorand batteries in the case of an electric powered trimmer, cooling andprolonging the life thereof. Directing air into the plane of therotating line in the direction of rotation reduces the relative velocitybetween the air and the line, reducing the drag on the line. Theaerodynamic features also preferably extend about the periphery of thehousing below the level of the line outlet apertures in the side of thehead to cooperate with the arcuate troughs and direct the air flowgenerated by the troughs into a substantially horizontal flow from thehead so as to maintain the forwardly directed air flow in and about theplane of the extended cutting line, further decreasing the drag on theline and maintaining the extended rotating line in a substantiallyhorizontal disposition to provide an even cutting of the vegetation andreduce the vibration of the line and the noise generated thereby.

In an improved embodiment of the present invention particularly adaptedfor enhancing the cooling effect of the trimmer head on the trimmerdrive mechanism, a generally curvilinear shroud is provided adjacent tothe upper surface of the trimmer head housing. The shroud defines aplurality of openings in an upper portion thereof spaced from andextending about the central axis of rotation of the trimmer head so asto be positioned below and is substantially adjacent to the drivemechanism of a rotary trimmer. The interior or inner surface of theshroud is configured to cooperate with the outer surface of the upperportion of the housing to define therebetween a plurality of closed,open ended, arcuate channels extending downwardly at a forwardinclination in the direction of rotation of the head such that duringuse, the rotation of the head and shroud causes air to be drawndownwardly through the openings in the upper portion of the shroud andinto and through the arcuate channels by the centrifugal force actingthereon. The air exiting the channels is directed outwardly anddownwardly therefrom at a forward inclination in the direction ofrotation of the head and into the plane of the rotating cutting line.The exterior or outer surface of the shroud is preferably provided withaerodynamic elements in the form of dimples to reduce the drag thereonduring use.

As in the prior embodiment, aerodynamic features are preferably providedabout the periphery of the housing below the level of the line outletapertures in the side of the head that cooperate with the channelsformed by the head and shroud and direct the air flow generated by thechannels into a substantially horizontal flow from the head so as tomaintain the forwardly directed air flow emanating from the channels inand about the plane of the extended cutting line, again decreasing thedrag on the line and maintaining the extended line in a substantiallyhorizontal disposition during use. Vibration and noise also are againreduced. However, by forcing the air passing through the arcuatechannels formed by the shroud and the upper surface of the housing tofirst pass downwardly through the openings extending about the upperportion of the shroud, the incoming air flow is concentrated about therotary trimmer drive mechanism, enhancing the cooling effect of the airon the drive mechanism. Also, by directing the air along the trimmerhead through the closed arcuate channels, as opposed to along openarcuate troughs as in the previously discussed embodiment, the volume ofair flow drawn onto and moved over the trimmer head housing and into theplane of the rotating line can be increased, further enhancing thecooling effect of the concentrated air flow on the rotary trimmer drivemechanism.

The outer surface of the lower portion of the housing in both of theabove-described embodiments is preferably is provided with a pluralityof patterned dimples therein to break up the air boundary adjacent thelower housing surface reducing the areas of laminar flow adjacent to thehead and thereby reducing the drag on the lower housing surface and theoverall drag on the head. The volume of air movement effected by thedimples is quite small so as to reduce the drag on the lower portion ofthe rotating trimmer head without disturbing the vegetation below thehead sufficiently to impair uniform cutting thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of the trimmer headof the present invention as seen from above.

FIG. 2 is a perspective view of the embodiment of the trimmer headillustrated in FIG. 1 as seen from below.

FIG. 3 is an exploded perspective view as seen from above of the variouselements comprising the embodiment of the trimmer head of the presentinvention illustrated in FIG. 1.

FIG. 4 is an exploded perspective view of the various elementscomprising the first embodiment of the trimmer head similar to FIG. 3but as seen from below.

FIG. 5 is a sectional view of the embodiment of the trimmer head shownin FIGS. 1-4, illustrating the spool and trimmer head housing before thecutting line is loaded.

FIGS. 6A and 6B are sectional views of the trimmer head as shown in FIG.5 illustrating the loading of the cutting line.

FIG. 6C is the sectional view of the trimmer head as shown in FIG. 5with the cutting line wound thereon.

FIG. 6D is a top plan view of the trimmer head shown in FIGS. 1-6Cillustrating the zone of outwardly and forwardly moving air generated bythe head during rotation thereof.

FIG. 6E is a side view of the trimmer head shown in FIGS. 1-6Cillustrating the downward air flow about the trimmer head drivemechanism on a gasoline powered rotary trimmer and the elevation andthickness of the outwardly and forwardly moving zone of air generated bythe head during rotation thereof.

FIG. 6F is a side view of the trimmer head shown in FIGS. 1-6Cillustrating the downward air flow about the trimmer head drivemechanism on an electric powered rotary trimmer and the elevation andthickness of the outwardly and forwardly moving zone of air generated bythe head during rotation thereof.

FIG. 7A is a bottom plan view of the interior of the upper portion ofthe housing of the trimmer head shown in FIGS. 1-6C.

FIG. 7B is a perspective view of the interior of the upper portion ofthe housing of the trimmer head shown in FIGS. 1-6C.

FIG. 8A is a top plan view of the interior of the lower portion of thehousing of the trimmer head shown in FIGS. 1-6C.

FIG. 8B is a perspective view of the interior of the lower portion ofthe housing of the trimmer head shown in FIGS. 1-6C.

FIG. 9 is a cross-sectional view of the lower portion of the housing ofthe trimmer head taken along the line 9-9 in FIG. 8A.

FIG. 10A is a bottom plan view of the trimmer head shown in FIGS. 1-6Cin the drive mode showing the relative positioning of the lower camfollowers on the spool with respect to the lower cams on the housingwherein the lower cam followers and cams are shown in dotted lines.

FIG. 10B is a bottom plan view of the trimmer head shown in FIGS. 1-6Cin the line winding mode showing the relative positioning of the lowercam followers on the spool with respect to the lower cams on the housingwherein the lower cam followers and cams are shown in dotted lines.

FIG. 11A is a perspective view of the spool of the trimmer head shown inFIGS. 1-6C.

FIG. 11B is a cross-sectional view of the spool of the trimmer headshown in FIGS. 1-6C and is taken along the line 11B-11B in FIG. 10.

FIG. 12A is a cross-sectional exploded view of the spool of the trimmerhead shown in FIGS. 1-6C as viewed along the line 12A-12A in FIG. 10 butprior to the insertion of the channel-forming inserts to illustrate aneconomical method of forming the spool.

FIG. 12B is a cross-sectional view of the spool of the trimmer headshown in FIGS. 1-6C and is taken along the line 12A-12A in FIG. 10illustrating the spool with the channel-forming inserts installed.

FIG. 12C is a cross-sectional view of the spool of the trimmer headshown in FIGS. 1-6C and is taken along the line 12A-12A in FIG. 10illustrating the spool with the channel-forming inserts installed andwith the cutting line extending through the line receptor channel in thespool.

FIG. 12D is a cross-sectional view of a spool for use in the embodimentof the trimmer head shown in FIGS. 1-6C and is of single-piececonstruction.

FIG. 13 is a bottom plan view of the trimmer head shown in FIGS. 1-6Cshowing the relative positioning of the upper cam follower with respectto the lower cam follower and with the upper cam follower and lineopenings being shown in dotted lines.

FIG. 14A is a side view of the spool of the trimmer head shown in FIGS.1-6C.

FIG. 14B is a front view of the spool of the trimmer head shown in FIGS.1-6C as viewed from the left side of FIG. 14A.

FIG. 14C is a rear view of the spool of the trimmer head shown in FIGS.1-6C as viewed from the right side of FIG. 14A.

FIG. 15A is a perspective view of the trimmer head shown in FIGS. 1-6Cas seen from below and with the cutting line loaded thereon.

FIG. 15B is a perspective view of the trimmer head shown in FIGS. 1-6Cas seen from below and illustrating the cutting line as it begins to bewithdrawn from the lower open portion of the line receptor channel.

FIG. 15C is a perspective view of the trimmer head shown in FIGS. 1-6Cas seen from below and illustrating the cutting line as it furtherwithdrawn from the lower open portion of the line receptor channel.

FIG. 16 is a perspective, sectional view of an alternate embodiment of aspool for use in the present invention.

FIG. 17A is a top plan view of the upper portion of the housing of thetrimmer head shown in FIGS. 1-6C and illustrating various dimensionalparameters of the aerodynamic troughs formed therein.

FIG. 17B is a side view of the upper portion of the housing illustratingvarious dimensional parameters of the aerodynamic troughs formedtherein.

FIG. 17C is a partial sectional view of the upper portion of the housingof the trimmer head shown in FIGS. 1-6C showing the configuration of theaerodynamic troughs formed therein.

FIG. 18A is a bottom plan view of the exterior of the lower portion ofthe housing of the trimmer head shown in FIGS. 1-6C.

FIG. 18B is a side view of the exterior of the lower portion of thehousing of the trimmer head shown in FIGS. 1-6C.

FIG. 19 is a top plan view of an alternate embodiment of the aerodynamicfeatures in the outer surfaces of the housing of the present invention.

FIG. 20A is a side view of another alternate embodiment of theaerodynamic features in a trimmer head of the present invention.

FIG. 20B is a side view of yet another alternate embodiment of theaerodynamic features in a trimmer head of the present invention.

FIG. 21 is a partial side view of still another alternate embodiment ofthe aerodynamic features in a trimmer head of the present invention.

FIG. 22 is a sectional view of one of the finger/thumb receivingrecesses in the lower end of the spool in the trimmer head shown inFIGS. 1-6C.

FIG. 23A is a perspective view as seen from above of the application ofthe present invention to a fixed line head.

FIG. 23B is a perspective view as seen from below of the application ofthe present invention to the trimmer head shown in FIG. 23A.

FIG. 23C is a bottom plan view of the upper housing portion of thetrimmer head shown in FIGS. 22A and 22B.

FIG. 24A is a top plan view of still another alternate embodiment of theaerodynamic features in a trimmer head of the present invention.

FIG. 24B is a side view of the trimmer head shown in FIG. 24A.

FIG. 25A is an exploded perspective view as seen from above of a drivemechanism for a rotary trimmer and an improved trimmer head assembly ofthe present invention comprising a shroud and the trimmer head shown inFIGS. 1-6C.

FIG. 25B is an exploded perspective view as seen from below of thetrimmer head assembly illustrated in FIG. 25A.

FIG. 26 is a side view of the trimmer head assembly illustrated in FIGS.25A and 25B.

FIG. 27A is an exploded partial sectional view of a drive mechanism fora rotary trimmer and the trimmer head assembly illustrated in FIGS. 25Aand 25B.

FIG. 27B is a partial sectional view taken along the line 27B-27B.

FIG. 28A is a side view of the trimmer head assembly shown in FIG. 26illustrating the downward air flow about the drive mechanism on agasoline powered rotary trimmer and the elevation and thickness of theoutwardly and forwardly moving zone of air generated by the head duringrotation thereof.

FIG. 28B is a side view of the trimmer head assembly shown in FIG. 26illustrating the downward air flow about the drive mechanism on anelectric powered rotary trimmer and the elevation and thickness of theoutwardly and forwardly moving zone of air generated by the head duringrotation thereof.

FIG. 29A is a top plan view of the shroud of the present inventionprovided with an alternate aerodynamic element formed in the outersurface thereof.

FIG. 29B is a side view of the shroud illustrated in FIG. 29A.

FIG. 30 is an exploded perspective view as seen from above of the shroudillustrated in FIGS. 25A and 25B and a trimmer head having a smoothcurvilinear upper housing surface.

FIG. 31 is an exploded perspective view as seen from above of analternate embodiment of the aerodynamic trimmer head assembly of thepresent invention.

FIG. 32 is a side view of a trimmer head embodying the present inventionwherein the shroud is formed as a portion of the trimmer head housing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now in detail to the drawings, a first embodiment of a trimmerhead 10 embodying the teachings of the present invention is illustratedin FIGS. 1-18B. Trimmer head 10 is a bump-feed type and is designed tobe mounted on the extended end of a rotatable drive shaft 12 on agasoline or electric powered rotary trimmer (not shown). Trimmer head 10comprises a housing 14, spool 16, coil spring 18 and drive bolt 20. Thehousing comprises an upper portion 14 a and a lower portion 14 b thatare releasably secured together about the spool 16. The drive and linefeeding mechanism employed in trimmer head housing 10 is similar to thatdisclosed in detail in U.S. Pat. No. 4,959,904 and the rapid lineloading and line replacement mechanism employed in trimmer head 10 isdisclosed in U.S. Pat. No. 7,797,839. However, the aerodynamic profileof the head 10 and the cooperative aerodynamic elements defined by theexterior surfaces of the head are novel. While primarily described belowin connection with a bump-feed type head having the above noted linedrive, feeding, loading and replacement features, the aerodynamicfeatures of the present invention can be employed in trimmer headshaving a wide variety of drive configurations, line feeding mechanismsand line loading and replacement systems.

In the illustrated embodiment of trimmer head 10, the housing 14 is of aslightly flattened, generally ellipsoidal configuration so as to definea relatively low profile aerodynamic shape. By way of example, a trimmerhead embodying the present invention and having the same configurationas trimmer head 10 defines a maximum height H of 2.750 inches and adiameter D of 5.600 inches. The upper portion 14 a of the housing isperhaps best illustrated in FIGS. 7A, 7B, 17A and 17B and includes anouter surface 22 defining a generally flat upper annular area 22 aextending about and projecting radially from a central opening 23disposed about the central axis of rotation of the trimmer head. Area 22a can include printed indicia thereon and merges at its outer perimeterinto an annular curvilinear surface 24 extending outwardly anddownwardly and terminating at its lower end in a more gradually curvedskirt portion 25 extending slightly past vertical as seen, for example,in FIG. 17B.

The interior of the upper portion 14 a of the housing defines acentrally disposed depending tubular extension 26 axially aligned withthe central axis of rotation of the head. Tubular extension 26circumscribes an axial channel 26′ extending downwardly from the centralopening 23 in the housing surface and defining a cylindrical upperchannel portion 26 a and a hexagonal lower portion 26 b. Channel 26′ isconfigured to receive the drive bolt 20 in a mating configuration withthe upper cylindrical portion 20 a of the bolt being disposed in theupper cylindrical portion 26 a of the channel and the hexagonal lowerportion 20 b of the bolt being disposed in the lower hexagonal portion26 b of the channel. The lower portion of the drive bolt and the tubularextension in the housing could also be square or otherwise configured toprovide the desired interference fit between the drive bolt and housing.

The drive bolt 20 preferably is secured within the tubular extension byutilizing the natural shrinkage of extension 26 during the cooling ofthe freshly molded head 10 about the bolt. The upper and lower portionsof the trimmer head housing 14 are preferably molded of a plasticmaterial with a polyamide (nylon 6), 15% glass reinforced material beingmost preferred. Objects molded of such materials will shrink as thefreshly molded material cools. An annular groove 20 c can be provided inthe drive bolt to enhance the interference fit between the bolt andhousing upon the shrinkage of the freshly molded plastic housingmaterial about the bolt and thereby to enhance the securement of thebolt to the housing. Other means for securing the drive bolt to thehousing also could be employed. The drive bolt 20 may define aninternally threaded cylindrical bore 20 d extending axially therethroughfor threaded engagement with the drive shaft of the trimmer.

The upper portion of housing 14 also defines a pair of opposed slots 30in the housing skirt 25. The slots are open at their lower ends and areadapted to receive a pair of opposed metal outlet eyelets 32 in a pressfitment. Perimeter portions 33 of the slots are radiused so that theouter ends of the eyelets fit substantially flush with the outer surfaceof the housing. A plurality of equiangularly disposed and outwardlyprojecting radial tabs 36 also are provided at the lower end of theskirt portion 25 of the housing for the securement of the lower housingportion 14 b to the upper portion 14 a, as will be described.

While the present invention is described herein in connection withtrimmer heads in which the cutting line exits the head through opposedopenings, the aerodynamic features of the present invention are equallyapplicable for use on trimmer heads having a single line outlet opening.Such heads are in widespread use on low end rotary trimmers whereinadequate torque is generally lacking and improved aerodynamics in theheads would be very beneficial.

The upper housing portion 14 a additionally includes an interiordepending vertical wall 38 outwardly spaced from tubular extension 26.As shown in FIGS. 7A and 7B, the wall 38 is configured to define fourpair of inwardly angled surfaces 40, each pair forming a projection 44that projects radially inwardly toward the central axis of rotation ofthe head at the center of tubular extension 26. Each pair of angularlydisposed surfaces 40 are offset by 135° and extend parallel to the axisof rotation of the head. The projections 44 formed by surfaces 40 definecam surfaces wherein the leading edge of each of the projections 44defines an upper cam 44 a (assuming counterclockwise rotation of thehead as seen from above the head) and the trailing surfaces on eachprojection define an upper slide surface 44 b. The surface of each ofthe cams is again parallel to the axis of rotation of the head.

The lower housing portion 14 b of the trimmer head 10 is perhaps bestillustrated in FIGS. 8A, 8B, 18A and 18B and defines an outer arcuateinclined surface 45 circumscribing an enlarged central opening 46 andmerging proximate its upper end at 45′ into a slightly curved and moresteeply inclined upper end portion 47. The uppermost surface of endportion 47 merges along a radiused surface 47′ into an upper generallyhorizontal annular surface 47″. The interior of the lower housingportion 14 b includes an upstanding annular interior wall 48 thatcircumscribes central opening 46, an annular interior surface 43 thatslopes upwardly from wall 48 to vertical surface 49 and an annularhorizontal upper housing support surface 51 that extends radiallyoutwardly from the upper end of all surface 49 to a steeply inclinedwall surface 53. Surfaces 51 and 53 are adapted to abut the lower endsurfaces of the upper housing portion 14 a upon the upper and lowerhousing portions being secured together.

A plurality of equiangularly disposed slots 50 (four being shown) aredisposed in the lower portion of the housing for receiving acorresponding number of locking tabs 36 on the upper housing portion 14a. Slots 50 extend vertically through upper end portions of inclinedsurface 45 exteriorly adjacent the interior housing support surface 51and are provided with narrow offset access portions 50′ as seen in FIGS.8A and 8B. To attach the upper housing portion 14 a to the lower housingportion 14 b, a locking tab 54 defined by a resilient cantileveredportion 24′ of the upper housing portion 14 a must first be aligned witha small protrusion 56 provided on the lower housing portion 14 b. Theuser then inserts the four locking tabs 36 of the upper housing 14 ainto the four slots 50 in the lower housing portion 14 b. The tab 54 isthen pressed radially inwardly and the housing portions 14 a and 14 bare pressed together, mating together the upper housing portion 14 a andthe lower housing portion 14 b such that the lower annular end surface25′ of the upper housing portion 14 a is disposed on the annular supportsurface 51 in the lower housing portion 14 b. The user then rotates theupper housing portion 14 a counterclockwise with regard to the lowerhousing portion 14 b, causing the locking tabs 36 to translate into theoffset portions 50′ of the slots 50. When the locking tabs 36 havetranslated completely into the offset portions 50′, the tab 54 that hadbeen pressed inwardly and then became biased outwardly against interiorwall surface 53 upon the initiation of the rotation of the upper housingportion, now is aligned with one of the slots 50, allowing thecantilevered portion 24′ of the tab to return to its original,unstressed extended position and project outwardly into the alignedslot, whereupon the upper housing portion 14 a is securely attached tothe lower housing portion 14 b.

The lower portion 14 b of the housing 14 also defines four equiangularlydisposed, upstanding projections 58 on the interior annular surface 43(see, e.g. FIG. 8B). Projections 58 each define a radially extending,upwardly inclined foot portion 58′ at the trailing end thereof thatmerges into an inclined surface 58″ which merges into an outwardlyprojecting portion 58′″ at the leading end of the projection 58(assuming counterclockwise rotation). The outwardly projecting portions58′″ of the projections 58 define vertical, angularly disposed walls 58a that function as lower cams as will be later described. The footportions 58′ and inclined surfaces 58″ on the projections define lowerslide surfaces and cooperate with lower cam follower surfaces formed onspool 16, as will be later described.

The spool 16 in trimmer head 10 defines an upper flange 60, a middleflange 61 and a lower flange 62 carried by and projecting radially froma cylindrical body portion 64 so as to define two annular storage areas66′ and 66″ between flanges 60 and 61, and between flanges 61 and 62,respectively, for carrying coils of flexible nylon cutting line 17wrapped about body portion 64 such that upon assembly, the end portions17′ of the cutting line will extend outwardly through the opposedeyelets 32 (see FIGS. 6C-6E). An annular chamber 68 is provided in thedepending tubular extension 26 in the interior of the upper housing 14 aabout the lower portion of the extension. Chamber 68 is open at itslower end and defines an upper spring abutment surface 70. A cylindricalchamber 69 having an open upper end is disposed about the central axisof rotation in the upper end of the spool and defines a lower springabutment surface 71. When head 10 is assembled, the tubular extension 26on the upper housing projects into chamber 69 in the spool and the coilspring 18 extends between and bears against the spring abutment surfaces70 and 71 as seen in FIGS. 5 and 6. A lower portion 72 of spool 16projects outwardly from body portion 64 and defines at its lowermost enda ground abutment surface 73.

As seen, for example, in FIG. 2 and as will be discussed later herein inmore detail, the lowermost surface 73 of the spool 16 is generallycurvilinear and is shaped so as to merge smoothly into the contour ofthe lower portion of the head as defined by arcuate surface 45 on thelower portion 14 b of the housing so as to provide the trimmer head 10with a relatively low profile and the lower portion of the head with arelatively smooth aerodynamic shape. Also, spool surface 73 is providedwith a plurality of depressions or recesses 77 adapted to convenientlyreceive the fingers and thumb of the user for rotating the spool withrespect to the trimmer head housing to load the cutting line onto thespool without interrupting the operative connection between the spooland the housing as also will be later described.

Spool 16 preferably defines a line receptor channel 74 extendingtherethrough from a first open end 74 a to a second opposed open end 74b and having an open accessible portion 74 c therebetween. In trimmerhead 10, the opposed openings 74 a and 74 b of the line receptor channel74 are located in the middle flange 61 and when the spool 16 is securedwithin housing 14, the channel openings are radially aligned with theeyelets 32 in the upper housing 14 a (see, e.g., FIGS. 5 and 6),enabling the cutting line 17 to be inserted into the line receptorchannel through one of the eyelets 32 without having to remove the spoolfrom the housing. The line receptor channel 74 extends radially inwardlyfrom the opposed channel openings 74 a and 74 b through flange 61, turnsdownwardly at 75 a and 75 b in relatively wide radius curves and extendsdownwardly through opposed interior portions of the lower spool bodyportion 72, outwardly through laterally spaced openings 74′ and 74″ in alower recessed area 76 in the lowermost surface 73 of the spool andtransversely across a recessed area 76 in the spool surface 73,interiorly of the gripping recesses 77 formed therein. The portion ofchannel 74 extending across the lower recessed area 76 of the spool isthe open or exposed portion 74 c of the channel providing access to theportion of cutting line 17 extending therethrough. Channel portion 74 cpreferably is defined by a concave surface or is of an inverted U-shapedconfiguration to assist in guiding the cutting line through the lowerrecessed portion 76 of the spool. Recessed area 76 extends transverse tochannel portion 74 c to facilitate gripping of the cutting lineextending thereacross and protect the exposed line in channel portion 74c during use.

The upper flange 60 on spool 16 defines an upper cam follower 80 on itsupper surface and the lower spool flange 62 defines a lower cam follower82 on its lower surface as seen in FIGS. 3, 4, and 11A. While otherconfigurations could be employed, both cam followers are preferably of asquare configuration, defining four perpendicular surfaces 80′ and 82′respectively, and are offset by 45° with respect to the central axis ofrotation of the trimmer head. The cam abutment surfaces 80 a and 82 adefined by the trailing surfaces of the upper and lower cam followersare again parallel to the axis of rotation of the head. The leadingsurfaces of the lower cam follower which define sliding surfaces 82 bmay be inclined upwardly proximate the corners thereon so as to providesmoother ratcheting if needed. Also, the leading surfaces of the uppercam follower may also be inclined downwardly to facilitate line feeding.Such a downward inclination of the trailing surfaces is particularlypreferable on the smaller heads where the length of each of the camfollower surfaces is shorter which otherwise might make the relativerotation of the spool and housing during line winding more difficult. Itmay also prove desirable to incline the trailing surfaces of the upperand lower cams. In the preferred configuration, the sliding surfaces 82b on the lower cam follower are defined by inclined ramps as seen inFIGS. 10A, 10B and 13 to provide a smoother ratcheting of the spoolduring the winding of the cutting line thereon due to the more gradualincline than that which would be provided by radiused surfaces.

During use in the drive mode, the lower cams 58 a on the lower housingportion 14 b are aligned with and abut the lower cam abutment surfaces82 a on the trailing surfaces of the lower cam follower 82 (see FIG.10A). The configuration of projections 58 provides a relatively largecontact area for cams 58 a. Accordingly, as the housing is rotated in acounterclockwise direction by the trimmer drive, the spool is rotatedwith the housing. In this drive position, the upper cams 44 a areupwardly spaced from upper cam follower 80 so that the driving force isgenerated solely by the lower cams. When the lowermost surface 73 of thespool is pressed or bumped against the ground, the spool 16 is forcedupwardly within the housing, disengaging the lower cam abutment surfaces82 a on the lower cam follower from the lower cams 58 a and bringing theupper cam abutment surfaces 80 a on the upper cam follower 80 intoalignment and immediate abutment with the upper cams 44 a on the upperportion 14 a of the housing 14 whereupon the driving force is effectedsolely by the upper cams. When the lower spool surface 73 is lifted fromthe ground, the coil spring 18 forces the spool downwardly, disengagingthe upper cam follower from the upper cams and re-engaging the lower camfollower with the lower cams. With the first embodiment of theinvention, with each bump on the ground effects a relative rotation ofthe spool and housing of 90° results, regardless of the duration of thebump. During this relative rotation, centrifugal force causes apredetermined amount of fresh cutting line to be paid out through theopposed eyelets 32 in the trimmer head housing.

To load the cutting line 17 about spool 16, the opposed open ends 74 aand 74 b of the receptor channel 74 are aligned with the eyelets 32 suchthat a single length of cutting line 17 can be inserted through one ofthe outlet eyelets 32 of the upper housing portion 14 a and into andthrough the adjacent aligned open end 74 a or 74 b of the receptorchannel 74. Printed indicia, such as the arrows 92 illustrated in FIG.15A, can be provided on the outer surface of the lower housing portion14 b and in the recessed area 76 in the lower end of the spool tofacilitate proper alignment of the line receptor channel with theeyelets 32 in the housing skirt. As the cutting line is pushed into theline receptor channel 74 through, for example, open end 74 b, the endportion of the line passes about the curvilinear channel portion 75 band downwardly through the channel and out the opening 74″ in therecessed area 76 in the lower end of the spool as illustrated in FIG.6A. The end portion of the line projecting through opening 74″ can thenbe readily grasped and pulled downwardly, causing more of the cuttingline to be drawn inwardly through the eyelet and the adjacent portion ofthe line receptor channel 74. The downwardly extending end portion ofthe line is then redirected inserted back up through lower opening 74′and pushed upwardly through the remainder of the channel 74 and outthrough the other channel end 74 a and the aligned eyelet. As thecutting line is pushed upwardly through the lower channel opening 74′,it is drawn along the exposed transverse portion 74 c of the channel andis directed by the surrounding channel wall outwardly through thechannel 74 and to and through the adjacent eyelet to the positionillustrated in FIG. 6B.

The cutting line 17 continues to be pulled through the trimmer head 10until the midway point on the length of cutting line 17 to be loadedonto the head 10 is disposed in the open or exposed portion 74 c of theline receptor channel. In this position, approximately equal lengths ofline project through each of the opposed eyelets 32. Alternatively, thetwo end portions of the length of cutting line to be loaded on the spool16 could each be inserted through one of the separate channel openings74′ and 74″ in the bottom of the spool and pushed upwardly through theirrespective channel portions and out through the opposed ends of thechannel 74 and aligned eyelets. To wind the line onto the spool 16, itis only necessary to rotate the spool forwardly with respect to thehousing, i.e., in the direction of rotation of the trimmer head 10during use in the drive mode.

To assist in the winding of the cutting line 17 on to the spool 16 suchthat the portions of the line projecting from each of the two eyelets isdrawn back into the separate spool storage areas 66′ and 66″ and wrappedabout the spool as illustrated in FIG. 6C, the opposed ends 74 a and 74b of the line receptor channel are configured by the middle spool flange61 to direct the opposed portions of the line into the different spoolareas. This can be accomplished by removing portions of the channel walldefined by flange 61 adjacent to the two channel ends such that lateralopenings 74 a′ and 74 b′ are formed in the side wall, communicatingchannel end 74 a with area 66′ and channel end 74 b with area 66″ asshown in FIGS. 14A-14C. By inserting one's thumb and fingers intorecesses 77 in the lowermost surface 73 of the spool and rotating thespool in a clockwise direction using recesses 77, while holding thehousing stationary with the head in an inverted position (i.e., with thelower spool end 73 facing upwardly), the portion of the trimmer line 17projecting from the open end 74 b of the line receptor is directed intothe upper spool storage area 66′ and the portion of the trimmer lineprojecting from channel end 74 a is directed into the lower line storagearea 66″ (see FIG. 14C). Other guide surface configurations could alsobe employed to direct the opposing line portions into the differentspool chambers or storage areas 66′ and 66″.

By recessing the portion 76 of the lower end of the spool through theexposed portion 74 c of the line receptor channel extends, the exposedline is protected when the rapidly rotating head is bumped against theground to pay out fresh lengths of line through the eyelets 32. Ifdesired, additional protection can be afforded by, for example, aprotective bridge, a removable cap or other protective element (notshown) that would allow the user to access the trimmer line extendingthereover in channel portion 74 c. Any such protective element should beconfigured so as to provide a continuous curvilinear surface consistentwith the contour defined by the lower spool surface 73 and the adjacentouter lower housing surface 45. Such a protective element may beparticularly desirable for use on abrasive terrain such as gravel.

When the spool 16 is gripped and rotated relative to the housing asdescribed above, the lower slide surfaces 82 b on the lower cam follower82 will contact the upwardly inclined foot portions 58′ and surfaces 58″on the lower projections 58 in the lower portion of the housing and rideupwardly over the inclined surfaces (see FIG. 10B), causing the spool totranslate upwardly with respect to the housing and compressing the coilspring 18. As the manual rotation of the spool continues, the cornerportions of the lower cam follower 82 can ride over and clear theleading ends of projections 58 in the lower portion of the housing,whereupon the spring causes the spool to snap downwardly such that thelower projections and lower cam abutment surfaces are again in planaralignment. Thus, this reciprocating movement of the rotating spool,which, although not necessary, is preferably employed in the presentinvention to provide for an even distribution of the cutting line in thetwo storage areas 66′ and 66″ about the upper body of the spool. As aresult, the lengths of line tend to roll over themselves and fill thetwo spool areas without becoming entangled on the spool. Because theupper slide surfaces on the upper projections 44 and the leading (slide)surfaces 80 b on the upper cam follower 80 are in abutment, it may provedesirable to incline the trailing surfaces 44 b of the upper projections44 and/or the leading (slide) surfaces 80 b of the upper cam follower 80to provide smoother rotation of the spool with respect to the housingduring the loading of the line.

The above description of the trimmer head 10 and its components is basedon using the head on a conventional rotary trimmer in which the gear box(not shown) typically imparts a counterclockwise rotation to the driveshaft 12 and thus to the trimmer head as viewed from above. If the headwere used on a trimmer without a gear box or with one that imparted aclockwise rotation to the head, the leading and trailing surfaces on thecams and cam follower abutment members would simply be reversed.Accordingly, the orientation of the cam features and slide surfacescould be reversed to accommodate a rotary trimmer in which the gear boximparts a clockwise rotation to the drive shaft 12.

The bump-feed mechanism provided by the cams and cam abutment surfacesneed not be limited to square cam followers. The same is true of trimmerhead 10. The upper and lower cam followers formed by upper and lowerportions of the spool, for example, could be three or five sided. Threeand five sided cam followers would cooperate with an equal number of camabutment members in the upper and lower housings as shown in thereferenced drawings. The function, cooperation and operation of suchcams and cam followers would be otherwise essentially unchanged fromthat described above.

In the embodiment of the spool employed in the trimmer head shown inFIGS. 1-6C and 11A-12C, the line receptor channel 74 is formed byaffixing a pair of channel forming or line guide inserts 90 in theinterior of the spool. Spool 16 is preferably formed by an injectionmolding process and by using inserts 90 to form the line receptorchannel 74, the cost of manufacturing the spool is substantiallyreduced. Alternately, the same channel configuration could be obtainedwithout the need for inserts 90 in a single-piece construction, albeitat a substantially higher cost. Such a spool 116 is illustrated in FIG.12D. Other than its method of manufacture, spool 116 is substantiallyidentical to spool 16. In the spool 16 (see, e.g. FIGS. 4 and 12A) apair of generally rectangular, radially spaced, axially extending, slots92 are provided in the interior of the spool. The slots 92 areconfigured to receive inserts 90 such that the end surfaces of the slotscooperate with inner end surfaces on the inserts to define the portionsof the line receptor channel 74 disposed with the body of the spool. Inthe embodiment shown in the drawings, each insert 90 defines an upperconcave end surface 91′ that merges along a curvilinear end surface 91″into a substantially vertical concave end surface 91′″. Upon affixinginserts 90 in slots 92, the concave end surfaces 91′-91′″ of the insertsand the adjacent interior surfaces of the spool thus define surroundingwall for the interior portions of the line receptor channel 74. Theinserts 90 and the spool 16, like housing 14, are preferably both formedof a polyamide (nylon 6), 15% glass reinforced material, although othermaterials could be used. Currently, the inserts 90 are molded separatelyfrom and prior to the spools to allow for a natural shrinkage of theinserts as the material cools. The inserts are then inserted into thefreshly molded spool in a relatively tight fitment such that thesubsequent shrinkage of the spool as it cools, locks the inserts inplace. It has been found that roughening the adjacent contract surfacesof the inserts 90 and the walls about slots 92 helps prevent anyslippage of the inserts during fabrication. Providing small crushableribs 90′ on the adjacent contact surfaces have been found to inhibit anyslippage of the inserts (see FIG. 12A). Also, a small lateral rib (notshown) can be provided on the extended end surfaces of the inserts thatare received in mating recesses formed in the outer walls of the slotsinto which the line guides are inserted. A depending foot portion (alsonot shown) can be formed at the lower outer end of each insert such thatupon insertion of the line guide insert into the freshly molded spool,the spool will cool and shrink not only against the insert, but aboutthe foot, enhancing the securement of the insert within the spool.Adhesives and other attachment means also could be used and, as notedabove and illustrated in FIG. 12D, the spool could alternatively bemolded of a single-piece construction.

In the event that the cutting line were to break during use proximateone of the eyelets 32, the trimmer line inwardly adjacent the breakretracts into the head so that additional fresh line cannot be payed outby simply bumping the head on the ground. With the present invention,the user can grasp the portion of the cutting line extending across theopen or exposed portion 74 c of the line receptor channel 74 and pullthe line downwardly as illustrated in FIGS. 15B and 15C. The downwardpulling on the line in a direction parallel, if not coincident to theaxis of rotation of the spool, will effect an unraveling of the line offthe spool, allowing all of the line to be pulled downwardly from thespool through the laterally-spaced openings 74′ and 74″ in the bottom ofthe spool. Thus, the old line can be removed from the trimmer headwithout having to split the head (remove the spool from the housing) orotherwise interrupt the operative connection between the spool and thehousing. The removed line or a new length of fresh line can then bere-loaded onto the head using the line receptor channel as earlierdescribed, again without having to split the head.

The spools illustrated in FIGS. 1-15C are dual area spools in which theportion of the line extending from one eyelet is wrapped about one areaof the spool or spool chamber (e.g. 66′) and the portion of the cuttingline exiting another eyelet is wrapped about another of the spool (e.g.66″). It is to be understood that the present invention could also beemployed with a single chamber spool such as that illustrated in FIG.16.

To enhance significantly the aerodynamics of the low profile shape oftrimmer head 10 during use, aerodynamic features, are provided in theouter head surfaces. By configuring the aerodynamic features so as tomove air outwardly from the rapidly rotating head in and about the planeof the extended cutting line and in a forward inclination in thedirection of head rotation (see FIG. 6D), the relative velocity betweenthe air and the rotating length(s) or portions 17′ of cutting line 17projecting from the head is reduced as compared to the length(s) ofrotating line moving through still air, significantly reducing theaerodynamic drag on the projecting line and thereby significantlyreducing the drag on the rotating head. As a result, the trimmer headcan run at a higher velocity with the same input drive or the samevelocity with a lower input drive, saving energy. This increase inefficiency is particularly significant for lower end rotary trimmershaving less torque. Also, the aerodynamic features that move the airoutwardly from the head to significantly reduce the drag on the line candraw that air downwardly about the axis of rotation from above the head(see FIGS. 6E and 6F) such that the air can first flow about the trimmerhead drive mechanism 11 on the rotary trimmer, which is positionedproximate the upper end of the trimmer head, providing a beneficialcooling effect on the drive mechanism (i.e., about the gear box 11′ of agasoline powered rotary trimmer (see FIG. 6E) or about the motor andbatteries (collectively identified at 11″ in FIG. 6F) of an electrictrimmer). To facilitate such cooling, the conventional gear box 11′ on agasoline powered rotary trimmer could be provided with exterior coolingfins 11 a and the cover 11 c surrounding the batteries and motor 11′ onan electric trimmer should be provided with a plurality of louvers 11 cor other appropriate openings therein to allow the cooling air flow topass therethrough. Further, by maintaining the air flow moved outwardlyand forwardly from the head in a generally horizontal disposition aboutthe plane of the extended cutting line such that the length(s) ofrotating cutting line projecting from the housing are continuouslytraveling within the forwardly directed air flow, not only is the dragon the rotating line significantly reduced, but also the line ismaintained in a substantially planar disposition to effect an evencutting of the vegetation. Vibration in the line and noise also arereduced.

In the above disclosed embodiment of trimmer head 10, the curvilinearouter head surface 24 defined by the upper portion 14 a of the trimmerhead housing 14 is provided with a plurality of uniformly spaced andangularly disposed arcuate troughs 100 formed into a turbine-likepattern about surface 24 (see, e.g., FIG. 17A). Troughs 100 arepreferably configured and arranged to draw air downwardly during usefrom above the central portion of the head onto the upper surface 24 ofthe rapidly rotating head, providing the above described cooling effecton the trimmer drive mechanism. The troughs 100 then drive the airoutwardly and downwardly from the head at a forward inclination in thedirection of rotation of the head (see FIG. 6D). As troughs 100 directair outwardly in a forward and slightly downward inclination, thetrimmer head 10 preferably positions the generally horizontal annularupper end surface 47″ of the lower housing portion 14 b outwardly of theopposed slots 30 in the upper housing portion 14 a such that surface 47″is disposed adjacent to and slightly below (e.g. about 0.125 in.) thebottom of the line outlet apertures in eyelets 32 so that the air abutsand is directed by surface 47″ outwardly in a relatively flatdisposition about the plane of the extended length(s) of cutting lineduring rotation of the head (see FIG. 6E). Thus, the troughs 100 willcreate a relatively flat zone of air 400, approximately 0.5 inchesthick, that projects at a forward inclination from the trimmer head (seeFIG. 6D), the lower boundary 402 thereof being substantially defined bythe positioning of surface 47″ on the upper end portion 47 of the lowerhousing 14 b. As a result, during use, the entire length(s), or at leastsubstantially the entire length(s) 17′, of the rapidly rotating cuttingline projecting from the housing 14 are effectively maintained withinthe forwardly moving zone 400 of air created by troughs 100 whichfurther enhances the effectiveness of the trough generated air flow inreducing the drag on the line. It also has been found that the air flowgenerated by troughs 100 reduces the aerodynamic drag on the upperportion of the housing, further contributing to the reduction of thedrag on the head during use. In addition, by directing the air flowabout at least substantially the entire length(s) of the extended lineas above described, the projecting line remains substantially planarduring use to provide an even cutting of the vegetation and, as notedabove, line vibration is reduced as is the noise generated by both theline and the rotating head.

While the annular upper end surface 47″ of the lower housing portion 14b is illustrated and described as being generally horizontal andinterrupted solely by locking tab slots 50 and troughs 104, it is to beunderstood that alternate surface configurations could be employed. Forexample, surface 47″ could be smooth, without any troughs or otheraerodynamic elements formed therein. The surface could be angledupwardly or downwardly to vary the elevation of the outwardly andforwardly moving zone of air 400 relative to the trimmer head to betteraccommodate different head configurations. Other modifications in thesurface 47″ might also be employed. While the surface could beeliminated as an aerodynamic element, it is preferably employed as abovedescribed and for the reasons stated.

In a presently preferred configuration, troughs 100 are generallyV-shaped in cross-section, inclined forwardly with respect to thehorizontal, and extend downwardly and forwardly (with respect to therotational direction of the head—counterclockwise as shown in thedrawings) along curvilinear paths from an upper inner portion of surface24 to a lower outer portion thereof. By way of example, a forward troughinclination of about 54° has been employed (see FIGS. 17A-C). Such aconfiguration has been found to move the air off surface 24 at a forwardinclination within the range of about 30 to 40 degrees in the directionof rotation as illustrated in FIG. 6D. As will be later described, thecurvature defined by troughs 100 can be a segment of a constant radiuscircle. Also, because sharp edges are preferably avoided on the surfacesof trimmer head 10 for aerodynamic reasons, such edges, including theedges and bottoms of the troughs, are typically radiused as shown, forexample, in FIGS. 1 and 2. Accordingly, the term “generally V-shapedtroughs”, as used herein, includes recesses that are curvilinear orgenerally U-shaped in cross-section.

Supplementing troughs 100 are a plurality of dimples 102, preferably ofa circular configuration, that are formed in the lower annular surface45 of the housing, circumscribing the ground abutment surface 73 ofspool 16. The dimples 102 in surface 45 are preferably arranged in aplurality of staggered, radially spaced, concentric rings, as seen inFIG. 18A, to minimize the flat surface areas between the dimples. Sopositioned, the dimples 102 break up the air boundary adjacent the lowerhousing surface on which they are formed, reducing the areas of laminarflow adjacent the head and thereby further reducing the drag on thehead. Dimples 102 will move less air than the troughs 100 in the upperhousing portion, but are preferably utilized on the lower portion of thehousing so as not to overly disturb the vegetation disposed below thehead and thereby adversely impact the uniform cutting of the vegetationwith the cutting line 17.

To further enhance the stability of the extended cutting line duringuse, aerodynamic elements 104, preferably in the form of relativelysmall, angularly disposed troughs or channels, can be provided in theupper end portion of lower portion 14 b of the housing. Troughs 104 areconfigured so as to offset the line lifting effect of the upper troughs100. Troughs 104 extend outwardly at a rearward inclination θ of about28 to 29 degrees (see FIG. 8A) about the annular surface 47″ at theupper end of the lower housing portion 14 b and through the adjacentradiused surface 47′, as seen in FIGS. 1 and 3. So positioned andconfigured, troughs 104 direct a relatively stable flow air outwardlyfrom the housing and slightly downwardly, under the extended cuttingline 17.

It has been found that by so directing the air flow about the lowerportion of the rotating housing and the extended cutting line utilizingthe dimples 102 and troughs 104, in combination with the forwardlyinclined outward flow directed by the larger troughs 100 on the upperhead surface 24 and by the upper end portion 47 of the lower portion ofthe housing, the drag on the head and particularly on the extendedcutting line is substantially reduced and the air pressure above andbelow the extended cutting line appears relatively balanced as theextended line remains substantially planar during use to provide an evencutting of the vegetation. Testing has shown that trimmer head 10 using0.095 in. diameter twisted nylon cutting line requires 24.5% less power(217 watts vs. 275) to drive trimmer head 10 at about 5,000 rpm than anidentically shaped head and equipped with the identical 0.095 in.cutting line but without troughs 100 and 104 and dimples 102. Atapproximately 7,000 rpm, the power savings was 24.5% (492 watts vs.652).

By way of example, in a trimmer head 10 having a maximum height of 2.750inches as measured along its central axis Y (axis of rotation) and adiameter of 5.600 inches, the troughs 100 formed in the arcuate uppersurface 24 of the head are configured and oriented so as to each definea radius of about 1.50 inches as measured from a point X as seen in FIG.17A, located on surface 24 1.438 inches below a horizontal lineextending through the axis of rotation of the head and along a firstvertical line located 0.573 inches to the right of a second verticalline extending through the axis of rotation of the head. Thirty-six suchtroughs are formed in surface 24 separated by an arc 10° as measuredfrom the axis of rotation. The troughs 100 are generally V-shaped incross-section and each of the troughs is angularly inclined toward thetrailing edge of the trough at an angle of about 54° as illustrated inFIGS. 17B and 17C. The troughs range from about 0.090-0.150 inchesacross and from 0.040-0.065 inches in depth. The spacing between thetroughs ranges from about 0.150-0.175 inches. The dimple pattern onlower surface 45, as noted above, is evenly and uniformly distributedand each dimple defines a diameter within the range of 0.090-0.125inches and a depth of 0.009-0.015 inches. The spacing between thedimples should be at a minimum and the molded dimples should have noundercut areas. The troughs 104 are fewer in number than troughs 100 inthe upper surface of the housing due to the presence of slots 50. In theillustrated example, there are 27 troughs 104 spaced about annularsurfaces 47 and 47′. The troughs 104 are angled about 10° apart at arearward angle of inclination of about 28-29 degrees. The troughs arespaced approximately 0.300 inches apart and each trough defines a widthof about 0.100 inch and a depth of about 0.025 inch. The angularorientation of the troughs 104 is illustrated in FIG. 8A.

The above dimensions and configurations of the trimmer head 10, troughs100 and 104 and dimples 102 are by way of example only. Other trough anddimple sizes and shapes and combinations thereof could also be employed.It has been found that while the above described angular disposition oftroughs 100 and 104 facilitate the molding of the upper housing portionof the head, it may be preferable to configure the troughs 100 on theupper surface of the trimmer head housing such that they do not trace aconstant radius but form a tighter curvature in the lower end portions100′ thereof as shown in FIG. 19. Additionally, dimples and/or troughscould be provided in the lower skirt portion 25 and/or upper end portion47 of the upper and lower housing portions as shown, for example, inFIGS. 20A and 20B. Again, other configurations and dimensional changesin the aerodynamic features could be employed.

Aerodynamic features in the form of protruding elements, ifappropriately configured spaced and sized, such as raised ridges 100Aand bumps 102A, could be employed in the present invention in lieu of orin addition to immersed cavities such as troughs and dimples to reducethe frictional drag on the head and line (see FIG. 21). As with the useof troughs and dimples, a variety of shapes and sizes of ridges, bumpsand/or other protruding elements should be suitable for use in the outersurfaces of the trimmer head to effect the desired air movement and theresulting reduction of drag on the head and line. Indentations in theform of troughs and dimples are preferred over protruding elements froma cost standpoint as the formation of cavities requires the use of lessmaterial, whereas the addition of air directing protrusions requires theuse of more material.

In certain instances wherein the cooling of the trimmer head drivemechanism may be of primary concern, the aerodynamic elements on atleast the upper head surface could be configured to enhance the downwardflow of cooling air about the trimmer drive mechanism while providinglittle or no reduction in aerodynamic drag on the trimmer head duringuse. Such an application could include large electric rotary trimmers inwhich the operating lives of the batteries and electric motors are ofprimary concern and could be meaningfully extended by adequate cooling.More typically, however, such elements would continue to provide both areduction in the aerodynamic drag on the head and a cooling air flow forthe drive mechanism.

As seen, for example, in FIGS. 2 and 22, and as noted above, thelowermost surface 73 of the spool 16 in trimmer head 10 has a pluralityof finger and thumb receiving recesses 77 formed therein for rotatingthe spool 16 with respect to the housing 14 to effect the winding of thecutting line 17 onto the spool in the manner described above. Tominimize the turbulence created by the rapidly rotating head in the areawithin and adjacent to those gripping recesses 77, the lower or bottomsurface 95 of each recess is inclined upwardly into the spool from thetrailing edge 95 a of the recess to the leading edge 95 b thereof so asto define a substantially vertically surface 95 c at the leading edge ofeach recess and a lower bottom surface 95 that slopes downwardly fromthe bottom of surface 95 to the lowermost surface 73 of the spool, asshown in FIG. 22. This configuration both provides a pushing surface 95c to enable the user to grip and rotate the spool within the housing inthe rotational direction of the head while holding the housingstationary to effect the winding of the line 17 onto the spool andprevents the trailing sides of the gripping recesses from functioninglike an air dam and trapping air within the recesses, creatingturbulence and slowing the rotational speed of the head. Thisconfiguration also allows the user only to wind the spool in onedirection obviating the need for directional indicia on the exposedbottom surface 73 of the spool where room is limited.

While the aerodynamic features of the present invention have beendisclosed in connection with a trimmer head 10 of the bump-feed typehaving a particular line feeding mechanism and line winding mechanism, avariety of such mechanisms could be employed with the aerodynamicfeatures of the present invention. Also, as noted earlier herein, thepresent invention is not limited to heads of the bump-feed type butcould be employed with manual heads, automatic heads and fixed lineheads.

FIGS. 23A-23C, for example, illustrate the use of the present inventionin a fixed line head 210. As seen therein, the aerodynamic elements inthe upper and lower housing portions 14 a and 14 b of the previouslydiscussed trimmer head 10 can be employed in the upper and lower housingportions 214 a and 214 b of the housing 214 of the fixed line head 210.Again, the upper and lower housing portions 214 a and 214 b areconfigured and mated together so as to provide head 210 with a generallyelliptical, aerodynamic low profile configuration. Because a fixed linehead does not include an interior spool, the profile of head 210 may beslightly flatter than head 10.

As with trimmer head 10, the upper housing portion 214 a of head 210 maybe provided with troughs 200 on the upper surface 224 thereof that canbe configured like troughs 100 in the upper portion 14 a of head 10.Similarly, the lower housing portion 214 b can be provided with aplurality of dimples 202 in the lower housing surface 245, that can beof the same configuration and positioned in the same general patternedarray as dimples 102 in the lower housing portion 14 b of head 10,except that as seen in FIG. 22B, dimples 202 can cover a larger surfacearea than dimples 102 as the available surface area is larger. Theaccess opening 264 in the underside of the housing portion 214 b on thefixed line head is smaller than the central opening 46 for the spool 16in the lower end of housing portion 14 b of head 10. The access openingis provided in fixed line head 210 to enable the user to grasp theinwardly extended end portions of the lengths of cutting line and topull the line inwardly through the eyelets 232 and out of the housingthrough opening 264 as will be briefly described. To provide thelowermost portion of the lower housing portion with a continuouscurvilinear configuration, a removable cap 265 is provided to coveraperture 264 to prevent the creation of turbulence proximate the lowerend of the head. The outer surface of cap 265 also can be provided withdimples 202, as shown in FIG. 23B.

The lower housing portion 214 b also preferably includes a plurality ofarcuate troughs 204 positioned in the upper end portion of the lowerportion 214 b of housing 210. As with trough 104 in head 10, troughs 204are configured so as to project in the opposite direction of the troughs200 in the upper housing portion (i.e., forwardly as opposed torearwardly) and extend through the adjacent radiused surface 247′ andgenerally horizontal surface 247″ to direct a relatively stable flow ofair outwardly from the housing and downwardly under the extended cuttingline, as do troughs 104 in head 10. As with head 10, various changes canbe made in the size, configuration and positioning of the aerodynamicelements in head 210.

While not part of the present invention, the mechanism for loading,gripping and replacing the cutting line 217 in head 210 is described indetail in U.S. Pat. No. 6,928,741 and illustrated in FIG. 23C. As seentherein, short lengths of cutting line 217 project through opposedeyelets 232 and into aligned radial channels 244 within the head 210.The lengths of line are held in place by a pair of spring-biased toothedcams 216 that press the inner end portions of the line against channelwalls 244′. To remove the line when it becomes damaged or worn, the lineis simply pulled inwardly and downwardly through the central opening 264in the lower housing portion 214 b of the head. Opening 264 is axiallyaligned with central area 48 in the upper housing portion, providingaccess to the end portions of the lengths of cutting line. Due to theangular configuration of the locking cams 216 and teeth 250 formedthereon, the cams allow for the sliding movement of the line inwardlythrough channels 244 to load the lengths of line on the head, hold theline in place during use and allow the line to be pulled inwardly forremoval and replacement.

While the present invention has been illustrated and described inconnection with a bump-feed head 10 and a fixed line head 210, thoseparticular heads were illustrated and described by way of example only.As noted earlier, the present invention is not limited to a particulartype or types of trimmer head or heads having a particular drive, linefeeding, loading or replacement mechanism. Also, as noted earlier,various changes and modifications also may be made to the aerodynamicfeatures of the present invention, including, but not limited to, theshape of the head and the shape, size and location of the aerodynamicelements. For example, very shallow troughs in the form of scoring, asopposed to the deeper cavities or depressions formed, for example, bytroughs 100, channels or dimples 102, could be employed in the outersurfaces of the head to reduce the drag on the head during use. Whilethe scoring may not move sufficient air to effect a reduction of thedrag on the cutting line during use, it could reduce somewhat the dragon the housing, increasing the speed of rotation and reducing vibration.An example of such a trimmer head 310 is illustrated in FIG. 24.

As in the prior embodiments, trimmer head 310 preferably defines anaerodynamic generally ellipsoidal profile, although, again, other headconfigurations could be employed. As seen in FIGS. 24A and 24B, theupper portion 314 a of the trimmer head housing 314 includes aerodynamicelements in the form of score lines 300 tracing a turbine-like pattern.The score lines 300 extend in a closely spaced uniform disposition aboutupper housing surface 324 such that they trace curvilinear pathsextending downwardly and rearwardly from an upper inner portion ofsurface 324 to a lower outer portion thereof, similar to troughs 100 oftrimmer head 10, except that the score lines 300 preferably form atighter curvature in the lower portions thereof, similar to the endportions 100′ of the troughs shown in FIG. 19. The lower housing portion314 b can also be provided with score lines 301 in the lower housingsurface 345. The score lines 301 formed in the annular surface of thelower portion 314 b of the housing preferably form a mirror image ofscore lines 300, extending upwardly and rearwardly with respect to therotational direction of the head as seen in FIG. 24B. As with thetroughs and dimples of the prior embodiment, other score line patternsand configurations could be employed to provide the desired aerodynamiceffect. While the size of the score lines also could be varied, by wayof example, such lines can be about 0.020 in. wide and 0.010 in. deepwith a radial spacing of about 0.200 in. at their midpoints. The edgesof the score lines 300 and 301 preferably are radiused at about 0.005in. to avoid the adverse aerodynamic effects created by sharp edges inthe outer surfaces of the head. As seen in FIG. 24, the score linespreferably are slightly tighter at their upper end portions than theirlower end portions and the opposite is true with respect to the scorelines in the lower portion of the housing which are more closely spacedat their lower ends.

An improved embodiment of the aerodynamic trimmer head of the presentinvention is illustrated in FIGS. 25A-28B. This embodiment isparticularly adapted for enhancing the cooling effect generated by thetrimmer head on the drive mechanism of the rotary trimmer during use.The improvement can comprise the same trimmer head configuration astrimmer head 10 illustrated in FIGS. 1-6C but additionally includes ashroud 500 to form a new trimmer head assembly. The shroud 500 isdisposed between the upper portion 14 a of the trimmer head housing 14and the drive mechanism 11 of the rotary trimmer and, as will beexplained, cooperates with the upper portion of the trimmer head housingto channel air therebetween downwardly and at a forward inclinationalong non-linear paths over the upper portion of the trimmer headhousing and outwardly therefrom in a similar manner to the open troughs100 or protuberances 100A of the prior embodiments to enhance theaerodynamics of the trimmer head, reduce the drag on the line and obtainthe other previously discussed benefits of trimmer head 10. However, inthis trimmer head assembly, the shroud 500 also cooperates with thetrimmer head to better concentrate the air being drawn downwardly by therotating head and shroud about the axis of rotation of the head and thusabout the drive mechanism of the rotary trimmer. Also, the head andshroud move more air than does trimmer head 10 alone. The larger andmore concentrated downward air flow, significantly enhances the coolingof the rotary trimmer drive mechanism.

In a preferred embodiment of shroud 500, the shroud includes an uppercentral support portion 502 that is disposed about a central mountingaperture 504 and defines an outer perimeter wall surface 505 connectedby a plurality of ribs 506 with an annular curvilinear body portion 507.An annular opening 508, which is spanned by ribs 506, is disposedbetween the upper annular support portion 502 of the shroud and thecurvilinear body portion 507 thereof. The shroud body portion extendsoutwardly and downwardly and terminates in a lower end 503. A pluralityof aerodynamic elements in the form of dimples 509 preferably are formedin the outer surface of the body portion 507 of the shroud to reduce thedrag on the shroud during use. Dimples 509, like the dimples 102 thatare preferably formed in the lower annular surface of the trimmer headhousing, are preferably of a circular configuration and are arranged ina plurality of staggered, radially spaced concentric rings to minimizethe flat surface area between the dimples. Thus, dimples 509 break upthe air boundary adjacent the surface on which they are formed, reducingareas of laminar flow adjacent the shroud and thereby further reducingthe drag on the trimmer head during use.

The underside of the upper support portion 502 of the shroud defines aflat lower annular surface 510 that rests atop the annular surface 22 aon the upper housing portion of the trimmer head housing and is heldthereagainst in a fixed disposition so as to rotate with the trimmerhead during use. The shroud can be secured in place on the trimmer headby a drive bolt or the drive shaft of the rotary trimmer, depending onthe trimmer configuration. In the trimmer configuration shown in thedrawings, the trimmer drive shaft 12 extends through the centralaperture 504 in the upper support portion 502 of the shroud and ashoulder 513 on the drive shaft bears against a recessed shoulder 511disposed about aperture 504 in the upper surface 512 of the shroud asthe drive shaft 12 threadably engages a drive bolt 20 in the trimmerhead, securing the shroud 500 in place on the trimmer head for rotationwith the trimmer head as seen in FIGS. 27A and 27B. The exterior uppersurface of the shroud body preferably defines a relatively flat, annularouter surface 514 radially spaced from the upper support portion 502that is adapted to be disposed about 0.030-0.050 in. from the lower endsurface of the trimmer head drive mechanism 11 to provide an adequateclearance between the rotating shroud and the stationary drivemechanism.

The curvilinear body portion 507 of the shroud defines a radius ofcurvature substantially similar to that of the annular curvilinearsurface 24 of the upper portion of the trimmer head housing. The ribs506 on shroud 500 extend in uniformly spaced disposition from wallsurface 505 on the upper support portion 502 of the shroud, outwardlyacross the annular opening 508 disposed between the wall surface 505 andannular surface 514 and along the interior surface or underside of thebody portion of the shroud, defining arcuate paths preferablysubstantially identical to the arcuate paths defined by the troughs 100in the outer surface 24 of the trimmer head 10.

The ribs 506 depend from the shroud body and define lower end surfaces506 a that abut the annular curvilinear surface 24 of the housing so asto partition the area between the shroud 500 and surface 24 on the upperportion 14 a of the trimmer head housing into a plurality ofsubstantially identical arcuate channels 518. In traversing the annularopening 508 in the shroud, the ribs 506 define channel inlet openings518 a for each of the channels 518. The channels 518 are thus defined bythe ribs 506, trimmer head surface 24 and the interior surface 507 a ofthe shroud body. Channels 518 extend downwardly from channel inletopenings 518 a to outlet openings 518 b in a turbine-like patternbetween the shroud and the housing surface 24 at a forward inclinationin the direction of rotation of the head.

The ribs 506 which define the sides of channels 518 diverge outwardly asthey extend downwardly along their curvilinear paths as shown in FIG.25B and vary in elevation from a maximum depth proximate the inclinedperimeter wall 505 of the upper support portion 502 of the shroud to aminimum depth, proximate the extended end 503 of the shroud as shown inFIG. 25B. In a preferred configuration, the decreasing depth (orelevation) of the ribs correlates with the expanding width of thechannels as the channels extend downwardly and forwardly along thesurface of the head such that the cross-sectional area along eachchannel is substantially constant throughout the length of the channel.Also, the channel inlet openings 518 a are sized such that the areaacross those inlet openings is substantially the same as the area acrossthe channel outlet openings 518 b adjacent to the extended end 503 ofthe shroud. By maintaining a substantially constant cross-sectional areaalong the entire length of each channel, abrupt fluctuations in airpressure and velocity are avoided during use to maximize efficiency ofthe rotating trimmer head during use. In that regard, the outerperimeter wall surface 505 of the upper central support portion 502 ofthe shroud, which defines a portion of the channel inlet openings 518 a,preferably is radiused so as to smooth the approximately 90° transitionof the downwardly flowing air through the channel inlet openings andinto the channel 518, thereby avoiding sharp corners and abrupt changesin direction that would adversely impact the air flow through thechannels and impair the efficiency of the trimmer head.

In use, the channels 518 function similarly to the open troughs of theprior embodiments, albeit more efficiently. The rotating ribs 506 andthe centrifugal force that is generated by the rotating head and shrouddraw air downwardly into the channels 518 and move the air through thechannels and outwardly from the head as previously described withrespect to trimmer head 10 to reduce the drag on the line. The shroud500, however, forces the downwardly drawn air to enter the channels 518through the channel inlet openings 518 a that are positioned about thecentral opening 504 in the shroud so as to be located below and adjacentto the trimmer head drive mechanism 11 on the rotary trimmer. Thus, aspreviously noted, the downwardly flowing air is more focused about thedrive mechanism, significantly enhancing the cooling effect of the airon the drive mechanism while the shroud cooperates with the trimmer headto continue to provide the previously discussed aerodynamic benefits ofthe trimmer head 10 when used without the shroud.

As previously noted, the cooling of the trimmer head drive mechanism 11in a gasoline-powered rotary trimmer can be facilitated by providing themetal gear box or casing 11′, which is disposed about the drivemechanism 11, with exterior metal cooling fins 11 a to increase the heattransfer surface area of the casing. Such fins also can be beneficiallyemployed with shroud 500 and are illustrated in several of the figures.In addition, some gasoline-powered rotary trimmers are provided with arelatively large mounting flange 11 d that projects radially from theunderside of the gear box or casing 11′. The configuration of shroud 500illustrated in the drawings is particularly adapted to mate with thegear box on such trimmers by sizing and configuring the annular surface514 extending about the upper portion of the shroud to accommodate theflange 11 d and including an upstanding wall 516 that extends aboutsurface 514 proximate the outer edge of the gear box flange 11 d,allowing free rotation of the shroud 500 with the head 10 unimpeded bythe stationary flange 11 d while wall 516 helps prevent debris frompassing between the shroud and the trimmer head flange and interferingwith the operation of the trimmer head. To accommodate such flanges andprovide access to the inlet openings 518 a of channels 518 below theflange 11 d, a plurality of openings 11 e are drilled or otherwiseformed in the flange 11 d in axial alignment with the channel openings518 a in the shroud whereby the downwardly drawn air can pass adjacentto the gear box and enter channels 518 unimpeded by the flange 11 d.When used with trimmers having flexible drive cables or other rotarytrimmers that do not have such a flange, the channel inlet openings 518a in the shroud would be exposed, not covered, and thus the need foradditional air access openings would not exist. Also, without anextended flange, like flange 11 d, the upstanding wall 516 on the shroudwould be positioned inwardly of the channel inlet openings 518 asubstantially adjacent to abut the lower perimeter edge of the trimmerdrive mechanism so as to allow free rotation of the shroud with thetrimmer head relative to the stationary drive mechanism while inhibitingthe passage of debris between the shroud and drive mechanism.

To facilitate the cooling of the drive mechanism of an electric trimmer,the cover 11 b surrounding the batteries and/or motor which, unlike thetypical gear casing on a gasoline-powered trimmer, does not contain asupply of lubricant, such as oil, and thus could and should be providedwith a plurality of louvers 11 c or other appropriate openings thereinto allow the cooling air to pass therethrough. Preferably, such louversor openings could be provided in both the upper and lower surfaces andin the side walls of the cover as shown in FIG. 28B. On those electrictrimmers wherein the batteries are not located proximate the motor wherethey can be cooled by the downwardly flowing air, the cooling air stillprovides substantial benefits by cooling the electric motor and thusextending the operating life of the motor. The maximum benefit of thepresent invention on electric-powered rotary trimmers, however, isobtained when the batteries are located proximate the electric motorwhere they also are subject to the beneficial cooling effects of thetrimmer head. Regardless of the type of drive mechanism on the rotarytrimmer, the objective is to direct the air drawn downwardly by therotating head and shroud over the available heat transfer surface(s) ofthe drive mechanism prior to entering channels 518. When practical, itis preferable to increase the area of the heat transfer surfaces, suchas with the addition of fins 11 a, and to provide access to suchsurfaces, such as with louvers 11 c.

Shroud 500 can be formed, preferably molded, of the same polyamide(nylon 6) glass reinforced material as the trimmer head. However, as theshroud is not typically subjected to being bumped against the ground orother hard surfaces, it could be formed with a lighter and a lessexpensive material such as ABS plastic or impact polypropylene toprovide a relatively rigid, lightweight and sufficiently durableaddition to the trimmer head. By way of example, with a trimmer head 10having the dimensions set forth in Paragraph 94 above, a compatibleshroud 500 could have a height of about 1.0 in. as measured along itscentral axis of rotation and a diameter of 5.25 in. The ribs 506 are0.25 in. in elevation at the channel inlets and decrease to an elevationof 0.07 in. at the channel outlets. The radius of curvature of the outerperimeter wall surface 505 at channel inlet openings 518 a is preferablyequal to the radial dimension of the adjacent annular opening 508, whichin the present example is about 0.25 in. Such dimensions will, ofcourse, vary with the size of the trimmer head.

While the various dimensions of the head and shroud can vary and theribs 506 on the shroud 500 need not be aligned in any particular mannerwith the troughs 100 on the upper surface 24 of the trimmer head 10 whenthe head and shroud are secured to the rotary trimmer, the curvilinearpaths traced by the depending ribs on the underside of the shroudreplicate the paths traced by the troughs 100 on the trimmer head.Otherwise, there would be a drop in efficiency. If one or more of theribs on the shroud were to cross over one of the troughs 100 on thehead, an air leakage would result, creating a drop in efficiency. Evenif none of the ribs were efficiency. If one or more of the ribs on theshroud were to cross over one of the troughs 100 on the head, an airleakage would result, creating a drop in efficiency. Even if none of theribs were to cross over a trough, if the ribs did not replicate thepaths traced by the troughs, the air flow through the channels would bedisturbed, resulting in an increased pressure drop through the channelsand a drop in efficiency. For the same reason, it is desirable that thelower end surfaces 506 a of the ribs abut head surface 24 throughout thelengths thereof to minimize air loss and that the cross-sectional areasof the channels 518 be substantially constant along the lengths thereofto minimize energy losses through fluctuations in air pressure andvelocity. The number of depending ribs 506 and thus the number ofchannels defined by the shroud is not believed critical, although thenumber of ribs on the shroud may depend on the size of the troughs 100on the trimmer head so that all of the end surfaces 506 a on the ribscan abut head surface 24 at corresponding locations to minimize airleakage. For a head having the dimensions set forth earlier herein, itis believed that approximately 8 to 16 ribs is preferable. Ten ribs 506and thus ten channels 518 are employed in the embodiment of the shroudillustrated in the drawings.

While not specifically noted above, it is also to be understood that theadditional aerodynamic features that are preferably employed in trimmerhead 10, such as dimples 102 and troughs 104, can be employed in thetrimmer head used with the shroud 500. Also, other aerodynamic featuressuch as troughs configured like the troughs 100 in the upper housingportion of the trimmer head 10, could be employed in the upper surfaceof shroud 500 if it is deemed necessary or desirable to move additionalair over the head and forwardly into the plane of the extended length(s)of cutting line. In such instances, the radial dimension of the upperend surface 47″ of the lower housing portion should be extendedsufficiently so as to defect the air driven by troughs in the shroudinto the forwardly moving zone of air at the desired angle (generallyhorizontal) to complement the air driven by channels 518. The size ofsuch troughs in the upper surface of the shroud would depend on theamount of additional air desired. The larger the troughs, the more airis moved but the greater the drag on the head. Also, by using relativelynarrow and shallow troughs, the air moved by the shroud would beminimal, but the drag on the upper surface of the shroud would bereduced. Thus, such troughs could be used on the shroud in lieu of orwith dimples 509. For example, such troughs could be only about0.03-0.08 in. across and have a depth of about 0.009-0.015 in. Such ashroud is illustrated in FIGS. 29A and 29B. Further, shroud 500 could beutilized to improve the cooling effects of trimmer heads havingprotruding aerodynamic elements in lieu of troughs and dimples such asthose illustrated in FIG. 21. While shroud 500 has been discussed inconnection with a trimmer head 10 of the bump feed type, the shroud,like the aerodynamic features on trimmer head 10, is not limited to aparticular type of trimmer head or to trimmer heads having a particulardrive, line feeding, loading or replacement mechanism. Nor is the shroudlimited to use with heads having the particular shape and/or sizesdisclosed.

While shroud 500 was developed to enhance the cooling effects of theaerodynamic trimmer head 10 on the drive mechanism of the rotarytrimmer, the shroud could be used with trimmer heads, like head 10Aillustrated in FIG. 30, not having the aerodynamic elements of head 10such as troughs 100, 100′, 104 and 200, dimples 102, 25 and 202 orprotuberances 100A and 100B. In such applications, the lower ends 506 aof the depending ribs 506 in the shroud 500 would abut the upper surface24A of the head 10A and cooperate therewith to form a plurality ofchannels 618 differing from channels 518 only in that channels 618 wouldhave a smooth or relatively smooth lower surface. Because the ribs 506effectively define substantially larger blade configurations for movingair than do the open troughs 100, the elimination of such troughs orother aerodynamic surface irregularities in the trimmer head housingshould not substantially impair the performance of the resulting headand shroud configuration. It is to be understood, of course, that theconfiguration of head 10A, like the configuration of trimmer head 10,could be varied and the shroud correspondingly reconfigured to mate withthe head and form the air flow channels therebetween as described.

As the shroud 500 in the above-described trimmer head assemblies isremovable from the trimmer head, the trimmer head could be readily used,if desired, without the shroud. If the shroud was used with a trimmerhead having aerodynamic features like trimmer head 10, the shroud couldbe removed and the head used above to obtain the benefits of theaerodynamic features of the head without the enhanced cooling effectsprovided by the shroud 500. Such an application will be useful, forexample, in extreme climate conditions where efficiency continues to beimportant but the additional cooling provided by the shroud may not beneeded.

In yet another embodiment of the present invention, the parts could beeffectively reversed such that the interior of the shroud 700 is smoothand the ribs 506 that depended from the shroud would be replaced withsimilarly configured upstanding ribs 706 found on the upper surface ofthe trimmer head 710. The two components would cooperate in the samemanner as previously described to provide a highly efficient trimmerhead assembly providing substantial cooling effects for the drivemechanism on a rotary trimmer. Such an embodiment is illustrated in FIG.31.

In all of the above embodiments, it is highly advantageous that theshroud be fixed in place relative to the trimmer head during use tomaximize the efficiency provided by the shroud. For situations in whichthere would be no advantage to be able to remove the shroud from thehead, the shroud and at least the upper housing portion of the trimmerhead housing could be permanently affixed together. The shroud, forexample, could be sonically welded or otherwise secured directly to theupper portion of the trimmer head as opposed to being held in place bythe threaded engagement of the head with the rotary trimmer. Such atrimmer head 800 is illustrated in FIG. 32. While it is believed thatthe shroud also could be molded with the upper portion of the housing soas to be an integral part of the housing, such a process may prove to beunduly expensive for mass production.

As seen from the above description, various changes and modificationscan be made in the present invention. Insofar as the above describedchanges and modifications and/or any other changes or modifications arewithin the purview of any of the appended claims, they are to beconsidered as part of the present invention.

What is claimed is:
 1. An aerodynamic trimmer head assembly for use inflexible line rotary trimmers that provides reduced drag on the line andcooling air flow for the trimmer head drive mechanism during use, saidassembly comprising: a trimmer head including a housing adapted to beoperatively connected to a rotary trimmer to effect rotation of thehead, said housing defining at least one opening therein for the passageof a portion of a length of line therethrough and an upper trimmer headsurface; a shroud removably connected to said trimmer head for rotationwith said trimmer head, said shroud defining an annular body portiondisposed above and extending along said upper trimmer head surface; anda plurality of laterally spaced ribs projecting from said shroud or saidupper trimmer head surface said ribs extending outwardly and forwardlybetween said body portion of said shroud and said upper trimmer headsurface along curvilinear paths from an inner portion of said shroud toan outer portion thereof so as to define a plurality of air channelsextending outwardly and forwardly between portions of said upper trimmerhead surface and said shroud along said paths defined by said ribs, saidchannels defining a plurality of channel inlet openings disposed about acentral portion of said shroud such that during rotation of said headand shroud, air is drawn downwardly through said channel inlet openings,into and through said channels and outwardly therefrom at a forwardinclination in a plane in which the length of line projects from thehousing thereby reducing aerodynamic drag on the line and cooling thedrive mechanism of the rotary trimmer.
 2. The aerodynamic trimmer headassembly of claim 1 including a plurality of dimples disposed in anouter surface of said body portion of said shroud.
 3. The aerodynamictrimmer head assembly of claim 1 wherein said upper trimmer head surfaceand said body portion of said shroud each defines an upper inner portionand a lower outer portion.
 4. The aerodynamic trimmer head assembly ofclaim 1 wherein said shroud defines a centrally disposed mountingaperture therein and said channel inlet openings are disposed about andproximate said mounting aperture.
 5. The aerodynamic trimmer headassembly of claim 1 wherein the transverse dimension across each of saidchannels increases as said channels extend outwardly and forwardlybetween portions of said upper trimmer head surface and said shroud andthe elevation of said ribs decrease as said ribs extend outwardly andforwardly between said upper trimmer head surface and said shroud. 6.The aerodynamic trimmer head assembly of claim 1 wherein said uppertrimmer head surface and said body portion of said shroud each definesan upper inner portion and a lower outer portion wherein the transversedimension across each of said channels increases as said channels extendoutwardly, forwardly and downwardly between portions of said uppertrimmer head surface and said shroud and the elevation of said ribsdecrease as said ribs extend outwardly, forwardly and downwardly betweensaid upper trimmer head surface and said shroud.
 7. The aerodynamictrimmer head assembly of claim 1 wherein the cross sectional area ofeach of said channels is substantially constant as said channels extendoutwardly and forwardly between portions of said upper trimmer headsurface and said shroud.
 8. The aerodynamic trimmer head assembly ofclaim 1 wherein said upper trimmer head surface and said body portion ofsaid shroud each defines an upper inner portion and a lower outerportion and wherein the cross-sectional area of each of said channels issubstantially constant as said channels extend outwardly, forwardly anddownwardly between portions of said upper trimmer head surface and saidshroud.
 9. The aerodynamic trimmer head assembly of claim 1 wherein saidshroud defines inner wall surfaces extending along said channel inletopenings, each of said inner wall surfaces defining a radius ofcurvature extending downwardly and outwardly to provide a smooth andgradual directional transition for the air entering said channelsthrough said channel inlet openings.
 10. The aerodynamic trimmer headassembly of claim 1 wherein said upper trimmer head surface and saidbody portion of said shroud each defines an upper inner portion and alower outer portion and wherein the cross-sectional area of each of saidchannels is substantially constant as said channels extend outwardly,forwardly and downwardly between portions of said upper trimmer headsurface and said shroud.
 11. The aerodynamic trimmer head assembly ofclaim 1 wherein the cross sectional area of each of said channels issubstantially constant as said channels extend outwardly betweenportions of said upper trimmer head surface and said shroud.
 12. Anaerodynamic trimmer head assembly for use in flexible line rotarytrimmers that provides reduced drag on the line and cooling air flow forthe trimmer head drive mechanism during use, said assembly comprising: atrimmer head including a housing adapted to be operatively connected toa rotary trimmer to effect rotation of the head, said housing definingat least one opening therein for the passage of a portion of a length ofline therethrough and an upper trimmer head surface; a shroud removablyconnected to said trimmer head for rotation with said trimmer head, saidshroud defining an annular body portion disposed above and extendingalong said upper trimmer head surface; and a plurality of laterallyspaced ribs projecting from said shroud or said upper trimmer headsurface said ribs extending outwardly and forwardly between said bodyportion of said shroud and said upper trimmer head surface from an innerportion of said shroud to an outer portion thereof so as to define aplurality of air channels extending outwardly between portions of saidupper trimmer head surface and said shroud along said paths defined bysaid ribs, said channels defining a plurality of channel inlet openingsdisposed about a central portion of said shroud such that duringrotation of said head and shroud, air is drawn downwardly through saidchannel inlet openings, into and through said channels and outwardlytherefrom at a forward inclination in a plane in which the length ofline projects from the housing thereby reducing aerodynamic drag on theline and cooling the drive mechanism of the rotary trimmer.
 13. Theaerodynamic trimmer head assembly of claim 12 including a plurality ofdimples disposed in an outer surface of said body portion of saidshroud.
 14. The aerodynamic trimmer head assembly of claim 12 whereinsaid upper trimmer head surface and said body portion of said shroudeach defines an upper inner portion and a lower outer portion.
 15. Theaerodynamic trimmer head assembly of claim 12 wherein said shrouddefines a centrally disposed mounting aperture therein and said channelinlet openings are disposed about and proximate said mounting aperture.16. The aerodynamic trimmer head assembly of claim 12 wherein thetransverse dimension across each of said channels increases as saidchannels extend outwardly between portions of said upper trimmer headsurface and said shroud and the elevation of said ribs decrease as saidribs extend outwardly between said upper trimmer head surface and saidshroud.
 17. The aerodynamic trimmer head assembly of claim 12 whereinsaid upper trimmer head surface and said body portion of said shroudeach defines an upper inner portion and a lower outer portion whereinthe transverse dimension across each of said channels increases as saidchannels extend outwardly and downwardly between portions of said uppertrimmer head surface and said shroud and the elevation of said ribsdecrease as said ribs extend outwardly and downwardly between said uppertrimmer head surface and said shroud.